I have done some professional lab research on this topic. (Sorry, I can't reveal who I was working for, or who was paying for it, but I can talk about the results. Don't ask.) I will add the caveat that we didn't study flourescent light, just sunlight. We could not find a predictable time threshold for the reaction. It is definitely based on the intensity of the light source, as well as the temperature. On a bright day at summer-time A/C room temperature, skunking could happen effectively instantaneously, but more often it takes an hour or more. Every beer (in a green bottle, that is) was skunked to flavor thresholds in less than two hours. They were skunked to instrumentation thresholds in minutes. Brown bottles doubled the time period. Double a few minutes is only a few more minutes. A bottle taken out of the refrigerator did not exceed flavor thresholds unless it was exposed long enough to warm to room temperature. We also only looked at one mass market lager, one I would not call bitter. I don't know the effect we would get with differing bitterness levels.